1. Field of the Invention
This invention relates to a light-receiving member used for an electrophotographic apparatus or the like, and an electrophotographic apparatus making use of the same. More particularly, it relates to a non-single-crystal silicon type light-receiving member that can faithfully reproduce fine lines and minute dots and also can obtain images with a good contrast and a very high image quality in image formation by an electrophotographic apparatus, a copying machine, an LBP, a printer, a display etc. utilizing electrophotographic technology, and an electrophotographic apparatus making use of the light-receiving member.
2. Related Background Art
Non-single-crystal silicon type light-receiving members have a high surface hardness, exhibit a high sensitivity to long-wavelength light of semiconductor lasers (770 to 800 nm) or the like and also are almost free from deterioration due to repeated use. Hence, they are highly valued and put into use especially as light-receiving members for electrophotographic apparatus such as high-speed copying machines and LBPs (laser beam printers) employing the above semiconductor lasers. Such non-single-crystal silicon type light-receiving members, and copying machines and image forming processes making use of them can be generally exemplified as follows:
FIG. 1 is a diagrammatic cross section of a typical light-receiving member. Reference numeral 101 denotes a conductive support made of Al or the like; 102, a charge injection blocking layer for blocking the injection of charges from the conductive support 101; 103, a photoconductive layer comprised of at least a material of a non-single-crystal silicon type and capable of exhibiting photoconductivity; and 104, a surface protective layer for protecting the photoconductive layer 103.
FIG. 2 schematically illustrates an example of an image forming process in a copying machine. Around a light-receiving member 401 that rotates in the direction of an arrow, a primary charging unit 402, an electrostatic latent image forming zone 403, a developing unit 404, a transfer medium feed system 405, a transfer/separation charging unit 406, a cleaner 407, a convey system 408, a charge elimination light source 409 and so forth are provided as occasion calls.
The light-receiving member 401, having been heated by a heater 423, is uniformly charged by the primary charging unit 402. Then, light which has been emitted from a light source 410 such as a halogen lamp or a fluorescent lamp, is irradiated on an original 412 put on a platen glass 411 and light reflected therefrom is led onto the surface of the light-receiving member through mirrors 413 to 416, a lens system 417 and a filter 418 and projected thereon to form an electrostatic latent image, and a toner is fed to this latent image from the developing unit 404 to form a toner image.
Meanwhile, a transfer medium P such as a sheet of paper or plastic is fed in the direction of the light-receiving member through the transfer medium feed system 405 having a transfer medium path 419 and a resist roller 422. Then, an electric field with a polarity opposite to that of the toner is imparted on its rear side and at the gap between the transfer/separation charging unit 406 and the light-receiving member 401. As the result, the toner image on the surface of the light-receiving member is transferred to the transfer medium P and at the same time the transfer medium P is separated from the light-receiving member 401.
The transfer medium P thus separated is passed through the conveying system 408 to a fixing unit (not shown), where the toner image is fixed, and then discharged from the apparatus.
In the transfer zone, the residual toner remaining on the surface of the light-receiving member without contributing to the transfer is conveyed to the cleaner 407 and is removed by a cleaning blade 421, so that the surface of the light-receiving member is cleaned.
The surface of the light-receiving member refreshed as a result of the cleaning is subjected to charge elimination exposure applied from the charge elimination light source 409 and is again subjected to the image forming process cycle.
Now, the non-single-crystal silicon type light-receiving member used in the image forming process as described above has not only the advantage that it has a high sensitivity to long-wavelength light as stated above (sensitivity peak: around 680 nm; sensitivity region: 400 to 800 nm), but also a satisfactory standard in practical use since it does not cause a lowering of image quality such as crushed characters or slim lines, in an instance where it is used in an electrophotographic image forming apparatus and copies of documents are taken in an office having normal temperature and humidity. However, it does not necessarily meet the recent requirements for an image quality comparable to that in printing or even higher than that.
More specifically, when the non-single-crystal silicon type light-receiving member is used in an electrophotographic process and very fine lines of about 100 .mu.m or less are reproduced in an environment of high temperature and humidity, e.g., 30.degree. C./80% RH, a sufficient density cannot be obtained and also line breadth may become larger in some cases. For example, in an attempt where a Chinese character "", having complicated strokes and a four-cornered boxy component ".quadrature.", is printed in a region of 2 mm square, its four-cornered boxy component may crush to make the character illegible. Similarly, in an attempt where a Chinese character "", having many strokes in the horizontal direction, is printed in a region of 2 mm square, the horizontal lines composing this character may blur to make the character illegible. Such a level of blurred outputs can not be said to be satisfactory for good resolution, and it follows that no high level of satisfaction can be achieved in some cases with respect to not only the level of image quality required in the field of printing industry, but, also the level of image quality required in offices. Such unsatisfactory results may lead to the conclusion that the image quality is substantially "unacceptable" for commercial copying. Conventionally, to avoid such problems, for example, heater (in FIG. 2, a heater 423) is provided inside the substrate of the light-receiving member and the heater 423 is electrified to raise the surface temperature of the light-receiving member to lower the relative humidity so that good reproducibility can be ensured. This method causes an increase in power consumption of the whole copying machine to bring about an economical disadvantage, but the power to the heater must be kept on even at night during which the copying machine is not used at all, in order to ensure satisfactory image reproducibility when first used in the morning and to ensure good image quality when used in an environment of high humidity. Accordingly, to save energy and natural resources, it has been deemed desirable to develop a light-receiving member requiring no heater.